In recent years, proposals and studies have been made to use a sheet-shaped object made of a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer, as an inner liner for a pneumatic tire (see Japanese patent application publication no. 2009-241855).
For actual use of the sheet-shaped object made of the thermal plastic resin or the thermoplastic resin composition obtained by blending the thermoplastic resin and the elastomer as the inner liner for the pneumatic tire, a manufacturing method is generally employed in which the laminated sheet including: the sheet made of the thermal plastic resin or the thermoplastic resin composition obtained by blending the thermoplastic resin and the elastomer; and the rubber (tie rubber) sheet cured and adhered to the sheet of the thermal plastic resin or the thermoplastic resin composition obtained by blending the thermoplastic resin and the elastomer is wound around a tire making drum and lap-spliced and is then subjected to step of cure-molding.
Consider, however, a case where a tire is manufactured by: winding the laminated sheet, which is made of the thermoplastic resin or the thermoplastic resin composition obtained by blending the thermoplastic resin and the elastomer and the tie rubber layer and which has been wound into a rolled shape, is pulled out and cut from the rolled shape by a desired length, around the tire making drum; lap-splicing the laminated sheet on the drum or the like; and then cure-molding the lap-spliced sheet. In this case, after the tire starts to be used for running, delamination may occur between the sheet of the thermoplastic resin or the thermoplastic resin composition and the tie rubber sheet cured and adhered to the sheet of the thermoplastic resin or the thermoplastic resin composition, which collectively constitute the inner liner.
To explain this with drawings, as shown in Part (a) of FIG. 2, a laminated sheet 1 including: a sheet 2 made of a thermoplastic resin or a thermoplastic resin composition obtained by blending a thermoplastic resin and an elastomer; and a tie rubber layer 3 is cut into a predetermined size (length) with an edge tool, for example. Then, both end portions of the laminated sheet 1 are overlapped with each other and lap-spliced on a tire making drum in such a way that a lap-splice portion S is provided and the laminated sheet 1 forms an annular shape.
Incidentally, when one laminated sheet 1 is used, both end portions thereof are spliced in such a way that laminated sheet 1 forms an annular shape. Meanwhile, when a plurality of laminated sheets 1 are used, both end portions of each of the laminated sheets 1 are spliced in such a way that the laminated sheets 1 form one annular shape as a whole. The cutting to the predetermined size may be performed in the state of the laminated sheet 1 obtained by laminating: the sheet 2 made of the thermoplastic resin or the thermoplastic resin composition obtained by blending the thermoplastic resin and the elastomer; and the tie rubber layer 3. Alternatively, the cutting may be performed in such a way that the sheet 2 and the tie rubber layer 3 are cut separately and thereafter laminated.
Then, other parts (not illustrated) necessary for manufacturing the tire are wound and a green tire is thereby formed. Thereafter, cure-molding is performed with a bladder.
As a result of the cure-molding, an inner liner layer 10 is formed which includes: the sheet 2 of the thermoplastic resin or the thermoplastic resin composition obtained by blending the thermoplastic resin and the elastomer; and the tie rubber layer 3, as shown in the view in Part (b) of FIG. 2 as a model. Around the splice portion S formed by overlapping, there are formed a portion where the sheet 2 made of the thermoplastic resin or the thermoplastic resin composition is exposed and a portion where the sheet 2 is buried inside the tie rubber layer.
The phenomenon of delamination between the sheet 2 of the thermoplastic resin or the thermoplastic resin composition and the tie rubber sheet 3 cured and adhered thereto occurs particularly in a vicinity 4 of the tip portion or the like of the sheet 2, at a spot shown in Part (b) of FIG. 2 where the sheet 2 of the thermoplastic resin or the thermoplastic resin composition is exposed. In the beginning, a crack develops, and then grows into the sheet delamination phenomenon.